An analytical method is known which comprehensively visualizes the amount of protein developed in tumor tissues or the like based on the mass signal intensity using matrix-assisted laser desorption/ionization (MALDI) and secondary ion mass spectroscopy (SIMS).
In the measurement of a living body sample by MALDI or SIMS, the sample constituent components are detected in an ionized state. In particular, the sample constituent components are detected as proton added molecules in many cases. Therefore, in order to increase the sensitivity of the detection of the sample constituent components, it is effective to add proton to the sample constituent components. As a method for promoting addition of proton to the sample constituent components, a method using the moisture contained in the sample and a method for giving moisture thereto from the outside are known. NPL 1 discloses a method for causing moisture to be adsorbed to the sample by cooling the sample in a water atmosphere to generate proton added molecules.
In SIMS, the utilization of cluster ions as a primary ion beam source for ionizing the sample has been examined. Heretofore, ions (single atom ions) whose atom is ionized has been used for primary ions. By the use of cluster ions with a high mass, damages to the sample can be reduced and the detection of the sample constituent components having a larger molecular weight can be achieved as compared with the case of using single atom ions with a low mass. PTL 1 discloses a method for performing mass spectrometry, using gas cluster ions as the primary ion beam source.